Many phone users would be horrified to discover a phone bill in the hundreds of dollars, but one woman was shocked when her telco requested payment of tens of thousands of dollars.

Nella Panetta returned from her Italian holiday to find a $75,000 phone bill that continued to grow.

The Perth resident thought that with international roaming enabled she would be able to use her phone until she bought an Italian one. But the agreement with her telco didn't come through, leaving her with a huge bill.

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She claims she was told that a $29 monthly plan would provide her with $900 of calls, texts and data, but it was immediately activated, rather than when she arrived in Italy as planned.

"While I was over there, I used my phone until I had a chance to ... get access to an internet USB stick and SIM card," she said. "I switched everything off; it just continued until I got home to Perth. It's still going on today."

She said she was shocked when she first opened her bill and saw how much she was expected to pay.

Ms Panetta said her bill was now $160,000 but had been told by the telco not to pay until the situation was resolved.

Ms Panetta's complaint topped the list in the Telecommunications Industry Ombudsman's most recent report, released on Thursday. Her dispute remains with the Ombudsman, Simon Cohen.

Other customers who had bills of $38,000 and $18,000 were among $8 million worth of disputed global roaming charges between July 2011 and last September.

The number of complaints has decreased, Mr Cohen said.

Many are about mobile services and bills of more than $5000.

The number of new complaints decreased by almost 19 per cent, he said, between April and June this year, and fell another 11 per cent between July and September.